The present invention relates to a drive assembly for auxiliaries of a motor vehicle, and more particularly, to a drive assembly having a driven shaft and a clutch arrangement by way of which the auxiliary is connected to the driven shaft, such as the fan of a motor vehicle engine.
DE-OS 22 54 390 shows the connection of a motor vehicle engine radiator fan by way of, for example, a magnetic clutch to the crankshaft of the engine. The magnetic clutch has a drive shaft which can be fixedly connected with the crankshaft, which forms the primary part of the clutch and can be coupled with a secondary part which is disposed in a freely rotatable manner and is connected with the fan wheel. A hysteresis disk is assigned to one clutch part and a magnet is assigned to the other clutch part. The working gap between the magnet and the hysteresis disk can be changed in the axial direction as a function of the rotational driving speed by way of a centrifugal governor. As a result, the transmissible torque can be increasingly lowered so that, at higher rotational engine speeds in which, as a rule, the driving speed is also higher, the driving power for the fan can be decreased.
DE-Gbm 88 11 100 also shows the connection of the radiator fan of a motor vehicle engine with the engine shaft by way of a fluid friction clutch. The fan, as a function of the cooling air temperature, optionally also as a function of the cooling water temperature, is driven faster or slower, specifically irrespective of how fast the engine is rotating. Both types of the aforementioned known constructions permit only a reduction of the rotational fan speed with respect to the drive shaft rotational speed.
FR 22 58 737 A also describes assigning rotatable coil arrangements to a shaft. These coil arrangements form a generator with a coil arrangement fixedly connected with the shaft. The generator can be driven, for example, by wind or water power. The use of an electric motor as a clutch for auxiliaries of motor vehicles, however, is not suggested by this known arrangement. DE-AS 10 70 282 describes an electric induction machine in which an electrodynamic clutch is connected between the induction machine and a power engine, with the two rotatable parts of the electrodynamic clutch carrying windings. A winding of the clutch and a polyphase winding of the electric induction machine in this case are connected to the same network. Such a development cannot be implemented for a drive assembly for an auxiliary of a motor vehicle.
It is an object of the present invention to provide a drive assembly such that the rotational speed for the drive of the auxiliary can be selected completely independently of the rotational speed of the driven shaft.
The foregoing object has been achieved in accordance with the present invention by providing a drive assembly in which an electric motor is used as a clutch arrangement. The stator of the electric motor is fixedly disposed on the driven shaft, and the rotational speed of the electric motor rotor is controllable by controlling the stator excitation with respect to the stator.
According to the stator excitation, the rotational speed of the rotor, on which, for example, the fan blades are fastened, can be reduced with respect to the rotational driving speed as was the case with prior art devices. With the present invention, it also becomes possible, however, to still increase the rotational rotor speed with respect to the rotational speed of the stator rotating along with the drive shaft so that, as a result, higher rotational speeds of the fan can also be implemented than can be provided by the drive shaft without switching on a high-expenditure transmission via clutches by merely using the electric motor as the clutch. The electric motor must only be configured for the difference of the maximally desired rotational fan speed and the rotational speed of the drive shaft because the stator rotates.
The rotor of the present invention can be placed directly onto the driven shaft. Between a housing receiving the driven shaft and the stator, in a further embodiment of the invention, an electronic power system can also be used for the control of the stator excitation which is expediently rotatably arranged on the driven shaft, is fixedly connected with the housing and configured to carry out the current transmission to the stator by way of slip rings.